The present invention relates to a radial antenna and a plasma processing apparatus using the same.
In the manufacture of a semiconductor device, plasma processing apparatuses are used often to perform processes such as formation of an oxide film, crystal growth of a semiconductor layer, etching, and ashing. Among the plasma processing apparatuses, a microwave plasma processing apparatus is available which produces a high-density plasma by introducing a microwave into a process chamber through a radial antenna. According to the characteristic feature of the microwave plasma processing apparatus, it has wide applications because it can stably produce a plasma even if the pressure of the plasma gas is comparatively low.
FIG. 7 includes views showing the arrangement of an example of a radial antenna conventionally used in the microwave plasma processing apparatus. FIG. 7(a) is a longitudinal sectional view of the radial antenna, and FIG. 7(b) is a cross-sectional view taken along the line VIIb-VIIb′ of FIG. 7(a).
As shown in FIG. 7(a), a radial antenna 130A conventionally used in the plasma processing apparatus is formed of two parallel conductive plates 131 and 132 which form a radial waveguide 133, and a ring member 134 which connects the peripheral portions of the conductive plates 131 and 132. A microwave entrance 135 is formed at the center of the conductive plate 132 to introduce a microwave from a microwave generator (not shown). The conductive plate 131 has a large number of slots 136, as shown in FIG. 7(b), to radiate the microwaves propagating in the radial waveguide 133 to a process vessel (not shown). The ring member 134 is made of a conductor.
The microwaves introduced from the microwave entrance 135 are radiated little by little from the large number of slots 136 into the process chamber while the microwaves propagate radially from the center toward the peripheral portion of the radial waveguide 133. The microwaves that have reached the peripheral portion of the radial waveguide 133 are reflected by the ring member 134 to return toward the center of the radial waveguide 133. The microwaves are gradually radiated through the large number of slots 136 into the process chamber while the microwaves propagate between the center and peripheral portion of the radial waveguide 133, so the microwaves are utilized for producing the plasma.
While the microwaves reflect at the ring member 134 in the radial waveguide 133, standing waves of a plurality of modes are formed, so a complex electromagnetic mode is produced in the radial waveguide 133. Hence, radiation from the radial antenna 130A to the process chamber becomes nonuniform, and a homogeneous plasma cannot be produced.
FIG. 8 includes views showing the arrangement of another example of the radial antenna conventionally used in the microwave plasma processing apparatus. FIG. 8(a) is a longitudinal sectional view, and FIG. 8(b) is a cross-sectional view taken along the line VIIIb-VIIIb′.
A radial antenna 130B shown in FIG. 8 is an improvement over the radial antenna 130A shown in FIG. 7, in which an electromagnetic absorbing member 139 made of a carbon-containing ceramic material or the like is applied to the inner wall of a ring member 134. The electromagnetic absorbing member 139 absorbs most of the microwaves that have reached the peripheral portion of a radial waveguide 133, so the microwaves are not substantially reflected toward the center of the radial waveguide 133. Accordingly, no complex electromagnetic mode is formed in the radial waveguide 133. Radiation toward the process chamber becomes uniform, so a homogeneous plasma can be produced.
With the conventional radial antenna 130B shown in FIG. 8, the microwaves absorbed by the peripheral portion of the radial waveguide 133 cannot be utilized for producing the plasma. The plasma production efficiency is thus poor. Since the electromagnetic absorbing member generates heat upon absorption of the microwaves, the peripheral portion of the radial waveguide 133, particularly the ring member 134, is locally heated to deform undesirably.